1. Field of the Invention
The present invention relates to an optical disc apparatus for reading video data from an optical disc such as a DVD (Digital Versatile Disc), and reproducing the video data as a moving picture on a monitor display apparatus.
2. Description of the Related Art
For recording the video data such as a moving picture taken by a video camera or a moving picture of a TV program received by a TV tuner on an optical disc such as the DVD, the video data are conventionally encoded in compliance with MPEG (Moving Picture Experts Group) standard. Similarly, for reproducing the video data recorded on the optical disc, the encoded video data are read out from the optical disc and decoded in compliance with the MPEG standard.
While the video data are read out from the optical disc, visual data are decoded in compliance with MPEG2 standard, and audio data are decoded incompliance with MP3 standard. Since the visual data and the audio data are independently decoded by different decoding circuits or decoder chips, it is necessary to output the audio data in synchronism with the visual data corresponding to predetermined AV (Audio/Visual) synchronization signals (this process is called “AV synchronization process”) for reproducing the moving picture on a screen of the monitor display apparatus.
FIG. 5 illustrates a configuration of a conventional apparatus shown in publication gazette of Japanese patent application 8-322043. Such the conventional apparatus inherently relates to a frame rate converter for converting frame rate of a moving picture. For example, when a video code recorded in a frame rate of 25 frames/sec is displayed in a frame rate of 30 frames/sec, video code data for one picture are repeated per five pictures so that six pictures are displayed in the same period as five pictures. Alternatively, when a video code recorded in the frame rate of 30 frames/sec is displayed in the frame rate of 25 frames/sec, video code data for one picture per six pictures are skipped without being decoded so that five pictures are displayed in the same period as six pictures.
In the conventional apparatus illustrated in FIG. 5, an AV synchronization controller 101 controls for synchronizing reproduction of the audio data with reproduction of the visual data. A frame rate converting controller 102 outputs alternative of a picture repeat request signal RP and a picture skip request signal RS corresponding to feeding of a decoding timing signal TD. A video timing generator 103 generates a display timing signal TH and the decoding timing signal TD corresponding to feeding of a video synchronization signal SY. A decoding controller 104 outputs a decoding start signal DS corresponding to feeding of the decoding timing signal TD. A video code buffer 105 temporarily stores video code data DV and serially feeds the video code data DV to a picture decoder 106. The picture decoder 106 decodes the video code data DV for one picture corresponding to feeding of the decode start signal DS and skips the video code data DV for one picture without decoding corresponding to feeding of the skip request signal RS.
The frame rate converting controller 102 includes a check signal generator 108 for generating a synchronization check timing signal TC, which shows the inherent decoding timing with no frame conversion, corresponding to feeding of a system clock SC. The AV synchronization controller 101 includes a check circuit 107 for checking the AV synchronization corresponding to feeding of a synchronization check timing signal TC. By such a configuration, the AV synchronization process can be executed with no relation to the frame rate conversion.
In the conventional optical disc apparatus, AV synchronization processing function such as the AV synchronization controller 101, the check circuit 107 and the check signal generator 108 are accomplished by hardware, so that the AV synchronization function is built in a chip with decoding function.
In recent years, corresponding to speeding up of working speed of a CPU (Central Processing Unit), the function, which is conventionally accomplished by hardware, can be accomplished by software, so that hardware of an apparatus tends to be simplified and made at a low-cost. Accordingly, for manufacturing the optical disc apparatus at a low-cost, a decoder chip with no AV synchronization function has been practically used.
When the audio data are recorded in the same time period as the visual data, the reproduction of sounds corresponds with the reproduction of moving picture, even though the video data are reproduced with no AV synchronization check in an optical disc apparatus using a decoder chip having no AV synchronization processing function. Alternatively, when the audio data are recorded in different period as the visual data, a phenomenon that the audio data are reproduced ahead of the visual data with respect to an audio gap where no audio data is recorded. Generally, auditory perception of human is more sensitive than visual perception. Thus, even when the audio data are reproduced a little ahead of the visual data, a TV viewer can be amused by the moving picture without unpleasant sensation. When a delay time of the reproduction of the visual data from the reproduction of the audio data becomes equal to or larger than 100 ms, discrepancy between the sound and the moving picture, which is called “lip sync”, can obviously be noticed, so that the TV viewer feels something is wrong.